Microwave energy is utilized in a variety of industrial processes for heating of various products in those situations when the product can be best processed by a heating procedure wherein the heat is generated within the material of the product itself rather than by a radiation of the heat from a point outside the material of the product as is accomplished with ordinary radiant heating. One such application of microwave heating is in a preheating process for the curing of rubber tires, the preheating process being utilized to raise the temperature of the rubber from room temperature to immediately below the range of temperature customarily utilized for vulcanizing the rubber of the tires. The microwave heating is particularly desirable in the preheating of very large tires such as those utilized on earth moving equipment wherein a single tire may weigh a few tons, the tread depth on such tires having a depth of almost one foot which militates against the use of radiant energy from a source external to the rubber because of the great thermal insulation qualities of rubber. In the heating of such tires, it is primarily the tread which need be preheated by the microwave energy since the sidewalls are sufficiently thin to permit the heat generated in the vulcanizing presses to penetrate through the rubber for uniform curing or vulcanizing of the sidewalls.
A problem arises in that large flexible objects such as the aforementioned rubber tire may have a complex shape which must be followed by a microwave feed horn so as to uniformly inject the radiant energy through the surface of the object into the interior of the object where it reacts with the material of the object to produce the heat, a precise scanning of the object by the microwave feed horn being most useful in maintaining a uniform heating of the material of the subject. More particularly, in the case of a rubber tire which is to be preheated prior to its being placed in the vulcanizing mold, the tire is preferably placed upon a mandrel for holding the tire to permit its being scanned, and for imparting to the tire a shape which generally follows a predetermined model. Because of the complex shape of certain objects to be heated and/or a shape which may differ from a predetermined model, radiation has been directed in the general direction of the object to be heated even though such a generalized directing of the microwave energy toward the object may result in locally uneven heating.